'Beringia Standstill' theorizes an extended stay on land bridge between continents

By Charlie Brennan, Camera Staff Writer

Posted:
03/13/2014 06:21:36 PM MDT

Shrub tundra near Eight Mile Lake, located in the foothills of the Alaska Range. An environment comparable to this may once have existed for thousands of years on the Bering Land Bridge. (Courtesy photo / Nancy Bigelow — University of Alaska Fairbanks)

The first Americans may have taken a break in their travels to this continent — one lasting several thousand years — according to a new study led by a researcher at the University of Colorado.

John Hoffecker is the lead author on a new commentary appearing in Science magazine that strengthens the theory that those who came to North America across the Bering Land Bridge from northeast Asia may have actually remained on that now-submerged plain for 5,000 years or more before spreading across this continent.

The theory addressed in the paper is not new.

First advanced as far back as 1997, then advanced further through mitochondrial DNA analysis in 2007 of Native Americans, it is well-established enough that it has a name — the Beringia Standstill, named for the land bridge once about 600 miles wide, connecting Siberia and Alaska.

Hoffecker and others now believe that several thousand people put down roots in central Beringia for at least 5,000 years. Pivotal to the premise is their belief that the region supported a shrub tundra vegetation, including some trees, providing wood fuel supplement to bone.

"If it's correct, it's telling us something very interesting and surprising about the origin of Native Americans," said Hoffecker, a fellow at CU's Institute of Alpine and Arctic Research. "Until these folks threw out the idea that Beringia had been an extended home, no one had really considered that.

"The idea that folks had lived in Beringia for an extended period of time, before dispersing through the Western hemisphere, and had been very isolated, that is a surprise and really startling thing to consider."

The "standstill" theory, Hoffecker said, envisions that a population of several thousand people occupied central Beringia during the last Glacial Maximum, when the Earth's ice sheets were at their greatest expanse, covering much of North America, Asia and northern Europe, between roughly 28,000 and 18,000 years ago.

Co-authors on the paper are Scott Elias of Royal Holloway, University of London, and Dennis O'Rourke of the University of Utah. Their paper seeks to bolster pre-existing work on the Beringia Standstill by further linking genetics to paleoecological evidence.

Accumulating mutations

Evidence from a 1997 study by two Latin American geneticists revealed a set of genetic mutations in mitochondrial DNA, which is inherited solely from the mother, which were accumulated after their dispersal from Asian parent groups in Siberia, but before their dispersal throughout North and South America.

That work was furthered by a University of Tartu team in Estonia, which sampled DNA from more than 600 Native Americans.

"If Native Americans had dispersed directly, if they had just they walked through, like crossing a bridge, then we would see a whole bunch of mutations, but they would vary as soon as the groups began to break up and disperse," Hoffecker said.

"But what we have here is the body of mutations that is a defining set, that is carried through North America. Yet it is distinct from the Asian source. It would have had to accumulate in one place, before everybody started to break up and go in different directions."

Hoffecker and his colleagues have now paired the genetic data with new evidence that central Beringia boasted a shrub tundra region, including some trees, during the last glacial maximum.

The existence of a fuel source that burns more slowly than bone, and data showing that the climate there and in adjacent land masses would have seen wetter and relatively warmer conditions due to North Pacific circulation patterns, together strengthen the case for the land bridge accommodating a longer stay by the earliest Native Americans.

"The paleoecological data, which I think most geneticists have not been familiar with, indicate that Beringia was not a uniform environment, and there was a shrub tundra region, or refugium, that likely provided habitats conducive to continuous human habitation," O'Rourke said, in a news release.

Side trips

Early Native Americans' extended Beringia sojourn doesn't mean that there wouldn't have been some side trips, the scientists believe.

"These areas to the east and west of the shrub tundra zone, presumably they were uninhabited year-round, but there is no reason folks couldn't have made forays into these areas on warmer days and warmer months, and had access to a vast hunting preserve — steppe bison, mammoth and horse," Hoffecker said.

"That actually might be a key as to how people were able to not only survive, but thrive. No competition. There's nobody else there to tap these resources."

Hoffecker believes future research on parts of Beringia that now are submerged, and also in eastern Siberia and western Alaska that are still above water, could eventually yield further evidence supporting one-time habitation by Beringia's "standstill" population.

"If people were concentrated in areas that are now under water, it should not be a surprise that we have not found their sites yet," he said.

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